A condition found in animals from the planet earth(primarily humans)in which the animal loses the ability to NOT speak every single word they are thinking. The verbal words are spoken about 1/trillionth of a second (actually faster than the speed of light) after the thought of the words in the brain itself.
Dad walking down street with 3 year old daughter bump into an extremely overweight acquaintance of dad's.
Dad:"Hi Lyndon."
Lyndon: "Hi Chuck."
Gracie(3-year-old daughter poking finger into Lyndon's large soft belly):"Mr. YOU have a FAT tummy!"
Gracie would at least momentarily be experiencing "Brainmouth".
A phrase often used by an angry spouse when their partner has described an inappropriate situation that they have been thinking about and the spouse would rather they didn't.
Peter: I'm just thinking about dem chicks! Dey were well fit! Banging!
Actively deleting data from one’s memory in protest of a real or imagined offense, trauma, or disappointment
The reason I’ve never gotten coffee at Julie’s Cafe before you suggested we meet up here is that a persistent case of brainpout caused my avoidance of anything with the name JULIE after a kid named Julie set a fire in my locker when I was fifteen.